1. Field of the Invention
The present invention relates to semiconductor memories, and particularly to architecture and organization of a dynamic random-access memory array and associated supporting circuitry for its high-speed reading and writing.
2. Description of Related Art
Semiconductor random-access memory devices or sub-systems using arrays of dynamic memory cells (e.g., 1-transistor/1-capacitor (1T/1C) cells) have consistently provided greater density and lower cost per bit than those using static memory cells (e.g., 6-transistor (6T) cells, or 4-transistor/2-resistor (4T/2R) cells). However, such dynamic random-access memory arrays have historically also been lower in performance when compared to static random-access memory arrays. Consequently, system designers have typically chosen dynamic memory arrays (e.g., commercially available dynamic random access memories, or DRAMs) when high density and low cost are required, such as for CPU main memory applications. Conversely, designers have typically chosen static memory arrays when the highest possible performance is required, such as for cache memory and high speed buffer applications. Examples of static memory array devices or sub-systems include commercially available static random access memories (SRAMs) and CPU-resident on-board cache memory sub-systems.
The reasons often cited for the lower performance of dynamic memory arrays include the destructive sensing of all memory cells common to the addressed word line (encountered in virtually all dynamic memory arrays) and the consequential need to restore data back into each sensed memory cell during the active cycle, the need to equilibrate bit lines and various other differential nodes and to precharge various circuit nodes between active cycles, and the requirement for periodic refreshing of all dynamic memory cells.
The need for ever-increasing memory performance at reasonable cost continues unabated. It is being driven by numerous advances toward higher frequency and higher speed applications. For example, the increasing bandwidth demands of computer networking and the internet, the increasing speeds of commercially available processors, and the proliferation of high-frequency wireless communication systems are all driving the need for higher performance memory sub-systems.
In spite of the performance gains of the last 20 years, there is an unfilled need for higher performance dynamic memory arrays which leverages the lower cost-per-bit usually associated with dynamic memory arrays into the performance realm and ease of use usually associated with static memory arrays.